Today data processing systems have multiwindow functions to perform a simultaneous processing of a plurality of processes under the control of a plurality of application programs.
The conventional multiwindow control method as described in JP-A-60,205,492 and JP-A-57,125,989 provides a scheme to discriminate visible windows. In such a method, a window to which data can be input or a current window is distinguished on the screen from a non-current window (wherein data cannot be input) by using a different brightness or luminance or by highlighting the data of the current window. However, a case where a window is completely covered by other windows and becomes invisible to the operator has not been considered in these patent applications. U.S. Pat. No. 5,179,655 provides a multiwindow control method an apparatus to process a window concealed by other windows when a plurality of windows are generated on the screen of a workstation. Namely, there is being provided a window display area taking precedence over all other display areas so that during operations of generating a new window or altering the window size of a beforehand generated window, etc . . . , any concealed window becomes represented by an icon placed in such window display area that an operator may recognize and identify as the concealed window.
However, it has not been considered, according to the prior art technology above, that a work station screen becomes very often hardly readable because the window display area taking precedence over all other display areas is rapidly filled with icons representing concealed windows. It becomes difficult for the operator to retrieve a particular concealed window of interest, especially given the necessary small size of icons. And yet, at any given time, an operator very frequently has a particular application associated to a particular window, which he considers to be the “main application at such time”, and which he would like to be able to retrieve rapidly from any secondary applications and windows.